1. Field of Invention
This invention relates to mimetic pseudopeptide analogs of the allatostatin neuropeptide family, and the use of these analogs for insect control.
2. Description of the Prior Art
The allatostatin family of insect neuropeptides inhibit the in vitro biosynthesis of juvenile hormone (JH) by the corpora allata of the cockroaches Diploptera punctata Blattella germanica (L) and Periplaneta americana (Belles et al., 1994, Reg. Peptides, 53:237-247; and Weaver et al., 1994, Comp. Biochem. Physiol., 107(c):107-127). In these pests, JH plays a significant role in development reproductive maturity, sex pheromone production and mating. Specifically, a reduction in endogenous levels of JH is critical to development of the adult stage from the nymph in the cockroach, whereas oocyte growth and maturation in adult females show a dependency on the presence of JH (Bendena et al., Allatostatins: Diversity in structure and function of an insect neuropeptide family. In: Beckwith et al., Eds., Neuropeptides in Development and Aging, pp. 53-66, Annals NY Acad. Sci. 814: 53-66: 1997).
Although the allatostatins can influence a number of physiological processes by virtue of their ability to modulate in vitro production of JH, the native allatostatins have held little promise as insect control agents. The major limitations of the allatostatins which have hampered their use for insect control include their inability to penetrate the insect cuticle, and their susceptibility to inactivation by peptidases in the hemolymph and gut and/or bound to tissues within the insect (Bendena et al., ibid).
Earlier structure-activity studies have shown that the C-terminal pentapeptide Xaa.sub.3 -Xaa.sub.2 -Phe-Gly-Xaa.sub.2 -NH.sub.2 (wherein Xaa.sub.1 occurs as any of Asn, Asp, Gly, Ser or Ala, Xaa.sub.2 occurs as Leu or Ile, and Xaa.sub.3 occurs as Tyr or Phe) is shared by all members of the Diploptera allatostatins, and represents the `active core` region or minimum sequence capable of eliciting inhibition of JH production in vitro (Hayes et al., Peptides, 15:1165-1171, 1994; Pratt et al., Biochem. Biophys. Res. Commun., 163:1243-247, 1989; and Pratt et al., Proc. Natl. Acad. Sci. USA, 88:2412-2416, 1991). The side chains of active core residues Phe, Leu and Tyr proved to be the most important for activity (Hayes et al., ibid). Recent studies have elucidated the primary catabolic cleavage sites of the allatostatins following incubation with hemolymph enzymes and with membrane peptidases in crude membrane preparations. Hemolymph enzymes primarily cleave the peptides in the N-terminal region outside of the pentapeptide core region and therefore, do not inactivate the allatostatins (Garside et al., Peptides, 18:17-25, 1997). However, membrane preparations of brain, gut and corpora allata cleave allatostatins at the C-terminus between residues Gly-Leu, with secondary cleavage occurring between the residue block Xaa.sub.3 -Xaa.sub.1 (Garside et al., Gen. Comp. Endocrinol., 108:258-270, 1997). Both of these cleavages disrupt the active core sequence and lead to completely inactive fragments.
The contents of each of the above-mentioned publications are incorporated by reference herein.